President Obama discusses developments in Boston with members of his national security team in the White House Situation Room on Friday. / Pete Souza, The White House

by David Jackson, USA TODAY

by David Jackson, USA TODAY

WASHINGTON - President Obama praised law enforcement Friday for their capture of a suspect in the Boston Marathon bombing, and vowed to find out the motives behind the attack that shook the nation.

"Obviously, tonight, there are still many unanswered questions," Obama told reporters at the White House, and said the families of this week's bombing and shooting victims deserve answers.

Saying he has ordered federal law enforcement agencies to get to the bottom of the case - including any international connections - Obama said that "we will determine what happened."

The president seemed to criticize some of the news coverage surrounding the attack and the investigation and asked Americans not to "rush to judgment" on the case, including possible motives. In an apparent reference to reports that the suspects are Muslim and have backgrounds in Chechnya, Obama said no one should be judged solely on their background and all defendants are entitled to a fair trial.

"When a tragedy like this happens, with public safety at risk and the stakes so high, it's important that we do this right," Obama said. "That's why we take care not to rush to judgment - not about the motivations of these individuals, certainly not about entire groups of people."

The president also said: "One thing we do know is that whatever hateful agenda drove these men to such heinous acts will not - cannot - prevail."

In the meantime, Obama asked Americans to honor the three people who died in Monday's bombing attack near the finish line at the Boston marathon, as well as the university police officer who was shot Thursday night in an apparent ambush by the two suspects.

One suspect later died after a shootout with police in the Boston suburb of Watertown; the second, wounded at some point, was apprehended shortly before Obama spoke on Friday night.

In praising the investigation, the president cited the "close coordination" among federal, state and local law enforcement, and said: "Boston Police and State Police and local police across the Commonwealth of Massachusetts responded with professionalism and bravery."

The president also paid tribute to the victims of this week's fertilizer plant explosion in West, Texas, saying, "I want them to know they are not forgotten." Obama also signed an emergency declaration Friday night authorizing federal aid to the devastated area.

The president added: "All in all, this has been a tough week, but we have seen the character of our country once more."

Obama had been constantly updated on the dramatic events in the Boston area throughout Friday, while White House officials remained mum about the manhunt for a second suspect in the bombing.

The White House canceled its daily news briefing while Obama conducted formal briefings in the afternoon and morning.

The president also phoned Massachusetts Gov. Deval Patrick and Boston Mayor Thomas Menino "to express his condolences for the MIT police officer who was killed overnight," said the White House in a statement.

"The President said that the entire country is behind the people of Boston as well as Massachusetts, and that the full force of the Federal Government will continue to be made available," the White House said.

FBI Director Robert Mueller, Attorney General Eric Holder and other officials went to the White House Situation Room at midmorning to brief Obama. He is also receiving updates from counterterrorism adviser Lisa Monaco, who led a formal briefing Friday afternoon.